The Android Operating System is based upon a modified version of the Linux kernel. It consists of 12 million lines of code including 3 million lines of XML, 2.8 million lines of C, 2.1 million lines of Java, and 1.75 million lines of C++. Just like the Linux kernel running on a desktop or laptop, the Java stack that sits on top of the kernel allow applications to be executed. Among the many applications, or apps, if you will, are the dialer app, and the phone app. They're just apps running on a computer, no different than Google Maps or Angry Birds or the Calendar.
Calling it a pocket computer that also happens to make phone calls is the most accurate description, because making and receiving phone calls is just one small subset of apps the computer will run. And because it's an open OS rather than a closed one, the user can customize it to work like they want it to.
That's why the Android phone is running 2:1 over the iPhone.